Anaesthetic agents

Question 1

Anaesthetics

- Defintion

Answer 1

Drug that is

• Lipid soluble
• Causes depression of brain activity in a specific order = Cortex—> midbrain—> spinal cord—> medulla

Question 2

Mechanism of anaesthetics

Answer 2

Very lipid soluble, mainly acts on ligand-gated channels

Stimulate inhibitory receptors

• GABA-alpha
• Glycine

Inhibit excitatory receptors

• Glutamate
• Nicotinic
• Serotonin

Question 3

Oxygen

• Function in anaesthetics
• Side effects

Answer 3

Always given with anaesthetics
- Contained in black cylinders with white shoulders/ piped

• Has to be chilled below 119 to be liquid

Side effects:
Oxygen free radicals

CNS convulsions

Pulmonary O2 toxicity

Retrolental fibroplasia

CO2 narcosis

Question 4

N2O

• Storage, description
• MAC
• Solubility, speed

Answer 4

Odourless- blue cylinder

Poor minimum alveolar concentration [MAC]

• 105%
• But good analgesic

Very soluble—> 35x than N2

Very quick on/onset

Question 5

Minimum alveolar concetration

Answer 5

The concentration of vapour in the lungs needed to prevent motor movement.

Question 6

N2O complications

Answer 6

Cardiorespiratory depression

Neuropathy

Bone marrow depression

Question 7

Isoflurane

• Chemical property
• Pros
• Cons

Answer 7

Inhaled agent- Halogenated ether

Pros

• Relatively cheap
• Stable
• Non-flammable
• MAC= 1.1%
• Very small proportion metabolised 0.2%

Cons

• Irritable to airway
• CVS and respiratory side effects

Question 8

Sevoflurane

• Description
• Pros
• Cons
• Chemical properties

Answer 8

Halogenated ether
- Most preferred inhaled agent to maintain anaesthesia after IV agent

Pros

• Non irritable to airway
• Quick onset/offset
• Very good MAC [2%], lower than Isoflurane
• CVS fairly stable

Cons

• Expensive
• More metabolised than isoflurane, but still fairly low [3%]

Question 9

Desflurane

• Description
• Pros and Cons
• Metabolism, MAC, speed

Answer 9

Highly fluorinated methyl ethyl ether

Pros

• Quick on and offset
• 0.02% metabolised

Cons

• Moderately expensive
• Irritant
• MAC 6.35%

Question 10

Thiopentone

• Chemical property
• Administration
• Use

Answer 10

Thiobarbituate
- Smell of garlic

Injected IV

Short acting, induces anaesthesia
- Antiepileptic

Cons

• CVS/RS depression
• Anaphylaxis
• Long half life[10 hours]
• Crystallises in the artery

Question 11

Profonol

Answer 11

Short acting anaesthesia

• Injected IV
• Used as substitute to thiopentone–> most preferred

Pros

• Very quick onset and offset
• Very quick redistribution and half life
• Does not accumulation greatly
• Also antiemetic and antiepileptic
• Can be used as total IV anaesthesia [TIVA]

Cons
- Painful to inject

Question 12

Muscle relaxant

Answer 12

Induces muscle paralysis
- Facilitates intubation and and manual ventilation

Can be:

• Depolarising–> Muscle contracts
• Non-depolarising–> Competitively binds to Ach receptors= blocks Na+ channels

Examples

• Suxamethonium
• Atracurium
• Rocuronium

Question 13

Suxamethonium

- Mechanism

Answer 13

Depolarising muscle relaxant

Mechanism
- Mimics the action of Ach, by binding to nicotinic receptors= causes release of Ca2+ from SR

• Prevents Ach from having an effect at the NMJ

Rapid effect and half life
- Broken down by cholinesterases

Question 14

Non-depolarising muscle relaxants

Answer 14

Competitively binds to Ach to block its action.
- Blocks Na+ channel for a longer duration that depolarising relaxant

Example:

• Rocuronium
• Atracurium